THE EFFECT OF SPACING ON SITKA SPRUCE WEEVIL DAMAGE TO SITKA SPRUCE

Tree diameter, height, form and number of stem defects were recorded in 26-yr-old plantations of Picea sitchensis established at 3 initial spacings (2.74 × 2.74, 3.66 × 3.66, and 4.57 × 4.57 m). These plantations were heavily attacked by Pissodes strobi from an early age. Denser plantations sustained a lower intensity of attack than the more open plantations. Although the 3 spacings had similar average number of stem defects per tree, trees in the close spacing had a significantly higher frequency of trees of good form relative to the more open plantations. As a management regime, it is recommended that Sitka spruce plantations be started at close spacing and precommercially thinned at age 25. By this age trees will average about 19 cm in dbh and 12 m in height, thus ensuring a first log of good quality. -from Authors